Assess & Decide

Assess - if there is traffic approaching from the right you must not move out if in doing so you would cause anyone to change speed or direction, if there are any pedestrians crossing the road you are turning into - STOP and wait until it is clear to proceed safely.
Decide - If there is closely approaching traffic or pedestrians crossing your path then you must not emerge - DO NOT ALLOW THE FRONT OF YOUR CAR TO PASS THE GIVE WAY LINES UNTIL YOU KNOW IT IS SAFE.
Before you do emerge make your final mirror checks to ensure the situation behind has not altered, look particularly for cyclists on your left.
Once you can see clearly into the road that you are joining and you are sure that it is safe to emerge then you should consider which gear is appropriate, the correct gear will depend on the speed of your vehicle. If the car is still moving at about walking pace then 2nd gear will be correct - if you have had to stop or practically stop before that you could se if it was safe then you will need to select 1st gear.

In this example the driver has had an early uninterrupted view he has looked, assessed the situation and because there is no need to give way and the there are no road markings requiring him to stop can begin to make his turn.